Document EP-A-0 544 576 describes an example of such an actuator.
The actuator described in that document gives entire satisfaction, but is nevertheless rather bulky, particularly because of the presence of its electronic control circuit which is distinct from the first printed circuit board.
Such bulk can be troublesome, particularly when the actuator is to be used in an environment where there is little room available, for example in a hydraulic anti-vibration support of the kind described in document EP-A-0 561 703.